Study On Mechanical Behaviors Of Frozen Cement-treated Silty Clay

Cement Stabilization and Artificial Ground Freezing Method are two common construction methods in geotechnical engineering.However,with more and more complicate geological conditions confronted in the practice as well as the shortcomings of these two methods,researchers and engineerers are planning to combine these methods,that is,reinforcing the ground with grouting first and then freezing them.This new method originates from these two methods,yet is evidently different from them.Considering few research on frozen cement-treated soils has been carried out by far,topic of this thesis,study on mechanical behaviors of frozen cement-treated Shanghai silty clay,was proposed.Unconfined compression tests of frozen cement-treated silty clay were employed first in this research project.Factors such as cement content,water cement ratio,curing periods and temperature were studied here to find the influences on the strength of the frozen soil by analyzing mainly the relations between strength,elastic modulus and these factors.And several fitting formula were obtained.The results showed that high amounts of cement,low water cement ratio,long curing periods and low minus temperature contributed positively to the strength of frozen cement soils.Besides,cement also reduced the plasticity of frozen soils while increased the brittleness and the failure modes and stress strain charactistics also changed due to cementation.It also revealed that the cement would make no difference when its content was less than 5%,but would receive a strength increase and brittleness improvement when the content reached 20%.And a high cement content like 40% would make the frozen soils go totally brittle.The research showed a range of cement content which would provide some references to civil engineerers.Apart from the experimental study,numerical simulation by Particle Flow Code PFC2 D was also executed to mimic the unconfined compression test of frozen cement soils with a 1.0 water cement ratio,28-day curing period and-10? environment.Displacement,stress,crack propagation and failure mode inside the specimen were analyzed from a microscopic perspective.A DEM model of frozen cement soils was found which revealed the feasibility for PFC2 D to simulate frozen soils.Results illustrated that the force was not evenly distributed in the sample during the test,instead,the stress mainly existed on the force chains which occurred on the bonded section between cement particles and ice bonding.This result proved that cementation was one factor for the strength growth.Crack propagation and stress distribution can also be analyzed by numerical simulation which contributes to the understanding of inner changes of frozen soils during unconfined compression tests.This research project shows that it is possible for civil engineerers to combine Cement Stabilization and Artificial Ground Freezing Method.It also brings software PFC2 D into future research on frozen cement soils to understand and study frozen soils microscopically.